Arnaud Bordes

Accurate modeling of battery thermal runaway is essential to reduce costly experimental testing, accelerate battery system development, optimize module and pack architecture, and ultimately improve safety of Li-ion batteries. While numerous modeling approaches currently coexist—including physics-based, lumped-parameter, and data-driven models—most focus primarily on thermal abuse as the initiating trigger and consider heat transfer as the only propagation mechanism. Overcharge-induced thermal runaway and propagation driven by electrical phenomena are comparatively underrepresented in current modeling frameworks. However, feedback from accident investigations shows that BMS failures can lead to such events. In addition, the parallel architectures used in some battery systems can result in the overcharging of cells within the same branch when a fault occurs in one of the cells.

The rapid growth of the electric vehicle market is driving the demand for lithium-ion batteries with higher energy densities. However, increasing cells size increases the consequences of a single cell internal short circuit (ISC), which remains a major safety challenge. ISCs can trigger thermal runaway, making their detection and evaluation critical for battery safety. Understanding ISC behavior is therefore essential as battery technologies evolve. Current literature mostly investigates ISC through abuse tests or external simulations, without precise control or repeatability. Few studies systematically optimize parameters to achieve reproducible ISC events and detailed electrical monitoring. The primary challenge lies in characterizing internal short circuits and distinguishing which ISC events are likely to lead to dangerous outcomes.

Le silicium est un matériau étudié depuis plusieurs années comme une sérieuse alternative au graphite dans les batteries Li-ion. Ce travail de thèse vise à développer des approches alternatives et complémentaires à celles déjà existantes afin de mieux comprendre les mécanismes de lithiation et de dégradation. L'analyse croisée entre plusieurs techniques, principalement FIB-ToF-SIMS, Auger, XPS et FIB-MEB, point central de l'étude, nécessite la mise en place de protocoles spécifiques prenant en compte la forte réactivité des échantillons lithiés. En premier lieu, un couplage entre ToF-SIMS et XPS sur des couches minces de silicium, permet de mettre en évidence la présence d'une phase riche en lithium ségrégée à l'interface entre la couche de matériau actif et le collecteur de courant en cuivre. Un mécanisme particulier de lithiation du silicium, basé sur l'existence de chemins de diffusion rapide pour le lithium, est suggéré. La réalisation de coupes FIB effectuées in situ dans la chambre d'analyse du ToF-SIMS sur des électrodes à base de poudre micrométrique de Si permet ensuite de proposer un mécanisme de lithiation analogue à celui mis en évidence précédemment. En outre, la présence de grains déconnectés du réseau percolant de l'électrode au cours du cyclage et piégeant le lithium est mise en évidence et contribue à la défaillance rapide de la batterie. Enfin, la méthodologie développée est appliquée à l'étude d'électrodes composées de Si nanométrique et de composite Si/C. Elle participe à l'établissement d'un modèle de croissance de SEI à la surface de grains de silicium nanométriques et permet d'identifier les raisons de la défaillance de ces électrodes.

Sodium-ion batteries are emerging as supplementary technology to lithium-ion batteries. This study focuses on investigating the thermal stability of Na3V2(PO4)2F3 (NVPF) || hard carbon (HC) sodium-ion cells through the lens of Solid Electrolyte Interphase. Differential Scanning Calorimetry demonstrated a clear increase in SEI stability formed with improved electrolyte formulations (NaFSI and additives). At cell level, Accelerating Rate Calorimetric tests were performed on pristine versus aged batteries. Ramp heating analysis revealed consistent thermal behavior, with SEI degradation initiating near 155 °C and thermal runaway (TR) triggering around 210 °C in both pristine and aged batteries. However, Heat Wait Search analysis on aged cells exhibited less severe TR compared to pristine batteries. The higher onset temperature observed in aged batteries was attributed to enhanced thermal stability of the re-formed SEI, while the reduced thermal severity was proven to be unlinked to the lower energy density.

As the use of Li-ion batteries is spreading, incidents in large energy storage systems (stationary storage containers, etc.) or in large-scale cell and battery storages (warehouses, recyclers, etc.), often leading to fire, are occurring on a regular basis. Water remains one of the most efficient fire extinguishing agents for tackling such battery incidents, and large quantities are usually necessary. Since batteries contain various potentially harmful components (metals and their oxides or salts, solvents, etc.) and thermal-runaway-induced battery incidents are accompanied by complex and potentially multistage fume emissions (containing both gas and particles), the potential impact of fire run-off waters on the environment should be considered and assessed carefully. The tests presented in this paper focus on analyzing the composition of run-off waters used to spray NMC Li-ion modules under thermal runaway. It highlights that waters used for firefighting are susceptible to containing many metals, including Ni, Mn, Co, Li and Al, mixed with other carbonaceous species (soot, tarballs) and sometimes undecomposed solvents used in the electrolyte. Extrapolation of pollutant concentrations compared with PNEC values showed that, for large-scale incidents, run-off water could be potentially hazardous to the environment.

As Li-ion batteries use is spreading, incidents in large energy storage systems (stationary storage containers, …) or in large-scale cell and battery storages (warehouse, recyclers, …), often leading to fire, are occurring on regular basis. Water remains one of the most efficient fire extinguishing agents for tackling those battery incidents and large quantities are usually necessary. Since bat-teries contains various potentially harmful components (metals and their oxides or salts, sol-vents…) and that thermal runway induced battery incidents are accompanied with complex and potentially multistage fume emissions (containing both gas and particles) the potential impact of fire run-off water on the environment should be considered and assessed carefully. The tests presented in this paper focus on the analysis of the composition of run-off waters used to spray NMC Li-ion modules under thermal runaway. It highlights that waters used for fire-fighting are susceptible to contain many metals, including Ni, Mn, Co, Li and Al mixed with other carbonaceous species (soot, tarballs) and sometimes undecomposed solvents used in the elec-trolyte. Extra-polation of pollutant concentrations compared with PNEC values showed that, for large scale incidents, run-off water could be potentially hazardous to the environment.

With the rise of electric vehicles (EVs) and thus lithium‐ion batteries (LIBs), the number of end‐of‐life (EoL) LIBs after their first life in EVs is about to increase significantly. These end‐of‐first‐life (EoFL) EV LIBs still have sufficient energy density for less‐demanding second‐life applications like stationary battery energy storage systems (BESSs) or mobile applications (e.g., forklifts, tools). Repurposing EoFL EV LIBs extends their lifespan, offering sustainability benefits and supporting several United Nations (UN) Sustainable Development Goals (SDGs). However, prevailing market entry barriers, such as high repurposing costs, little information on battery history and aging, or lacking performance indicators, hinder the widespread implementation of second‐life applications. Thus, this study aims to identify preconditions for considering and selecting useful EoFL LIBs and to determine key performance indicators (KPIs) to minimize economic risks for a successful second‐life market launch. KPIs were rated according to importance using a Likert scale, and reference values were introduced. A mixed‐methods approach, using expert interviews, an exploratory workshop, and an online survey, was applied. Twelve important preconditions were identified, with the “availability of information on battery specification” and “compliance with standards and regulations” considered very important. In addition, 12 KPIs were derived, covering six economic, three environmental, and three technical and safety‐related indicators. The KPIs “state of safety (SoS)” and “resource savings (R_sav)” were rated as highly important. Overall, the findings provide performance measurement guidance for repurposing companies, facilitating the market launch and adoption of second‐life applications. Future research can build on these results and investigate variations among different battery types, ultimately promoting a circular economy.